The present proposal is addressed to the mechanism by which calcium fluxes into and out of sarcoplasmin reticulum are controlled. The mechanisms underlying the transition between calcium influx and efflux in SR will be studied. Effects of various ionophores and drugs, including local anaesthetic agents will be examined. The possibility that altered surface charge on these membranes is responsible for transitions between calcium influx and efflux will be examined. The role of the calcium pump ATPase protein in these transitions will also be studied.